1. Field of the Invention
The present invention relates to methods for production of optical fiber connectors and, more specifically, to a method for production of a plug ferrule assembled in a plug which, in combination with an adaptor, comprises an optical fiber connector produced of a plastic. And a method for production of a sleeve assembled in an adaptor which, in combination with a plug, constitutes an optical fiber connector produced of a plastic.
2. Brief Description of Prior Arts
An optical transmission system absolutely requires equipment for connection of optical fibers or an optical fiber connector. In view of an increasingly larger potential demand assumed in the near future for optical fiber connectors, it is required to develop an optical fiber connector which is light in weight and which is easy to assemble and which can be produced at a low cost.
Included in the major functions required for an optical fiber connector are that it allows precise butting arrangement for the ends of optical fibers to be connected with each other between the ends of the cores thereof which ordinarily have a diameter of several ten micrometers and that it readily keeps the precisely butted position under any environmental condition. In other words, it is essential to precisely arrange two optical fibers to be connected to each other within a radial tolerance of several micrometers. Therefore, the performance of a plug ferrule with which the optical fibers are positioned, is an important parameter which determines the performance of an optical fiber connector. Particularly, the quality of the material of which the plug ferrule is produced and the dimensional accuracy of tolerance with which the plug ferrule is produced are important to allow the plug ferrule to satisfy the foregoing requirements.
An exemplary method, available in the prior art, for production of such a plug ferrule is disclosed in a Japanese patent application published under the Laying-open No. 55-67714 in Japan. A plug ferrule produced employing the method available in the prior art, is provided with a capillary having a small hole of which the diameter is slightly larger than the diameter of optical fibers to be connected and which is bored at the center thereof, the capillary being, fitted in a hollow metal collar, after it is inserted in the metal collar. The capilary having a cylindrical shape is produced by machining the internal and the external surface of a cylinder made of a sintered material e.g. some of the ceramics, after a center hole is bored in the cylinder. The metal collar is produced by means of precision machining. Thereafter, the capillary is fitted in a hole of the metal collar. The external surface of the metal collar is machined, while the metal collar is rotated centering around the small hole of the capilary. The foregoing method is effective to produce a plug ferrule which has an accurate external diameter and which has a low amount of eccentricity of the small hole in relation to the external surface of the plug ferrule. However, the foregoing method, available in the prior art, is inevitably involved with a drawback in which a high grade of machining technique employing extremely expensive machinery is required, because high precision machining applied to a hard material such as some of the sintered materials or ceramics is essential for the method. Further, the method is involved with drawbacks in which the productivity is low and the production cost is expensive.
Various efforts have been used for development of methods for production of a plug ferrule employable for an optical fiber connector in which plastics are employed as the material, for the ultimate purpose of lessening the production cost of the plug ferrule. For example U.S. Pat. Nos. 4,107,242 and 4,173,389 disclose a method for production of a plastic plug ferrule which is based on an idea to employ a metal mold employable for an insertion molding process and a jig. Namely, the method comprises a step to set an optical fiber in a metal mold and a step to inject some quantity of epoxy resin into the mold, for the purpose to form a mass containing the optical fiber and the plug ferrule in one body. Unfortunately, however, this method can not be free from a drawback in which a plug ferrule must be connected with an optical fiber prior to shipment, because the foregoing method is allowed to be employed only at a factory rather than under a field condition. Further, since the process for forming a mass containing an optical fiber and a plug ferrule in one body in accordance with the foregoing method is rather complicated, the foregoing method is not appropriate for mass production.